Process of forming a biaxially oriented thermoplastic tube including the formation and severance of a bubble forming a radially outwardly flared leading tube end

ABSTRACT

A process of forming biaxially oriented tubular articles by repeatedly performing a cycle of operations which includes engaging a thermoplastic tube by a first clamping member over a first region at a trailing end of the tube and engaging the tube by a second clamping mechanism over a second region at a spacing from the first region so as to define between the clamping mechanisms a portion of the tube to be longitudinally stretched and radially expanded; moving the clamping mechanisms apart to stretch the tube portion therebetween longitudinally; admitting pressure fluid into the tube portion to expand it radially and form a biaxially oriented bubble adjacent the leading end of the tube, and severing a substantial part, but not all, of the bubble from the tube to form the tube with a radially outwardly flared end as the leading end of the tube for the succeeding cycle of operations.

This is a division of application Ser. No. 700,306, filed Feb. 11, 1985and now abandoned, which is a division of application Ser. No. 574,615,filed Mar. 7, 1984, now U.S. Pat. No. 4,547,416, which is a division ofapplication Ser. No. 322,380, filed Nov. 17, 1981, now U.S. Pat. No.4,447,199.

FIELD OF THE INVENTION

This invention relates to thermoplastics articles, and methods andapparatus for making them. In particular the invention concernsthermoplastics articles which are tubular and of which thethermoplastics material is, at least in part, biaxially oriented to givethe articles enhanced physical characteristics.

BACKGROUND OF THE INVENTION

It is well known to form shaped articles from a thermoplastics materialby extruding a tube of the thermoplastics material, repetitivelyenclosing a length forming the end of the extruded tube within a mouldcavity, separating the tube lengths from the parent tube, and afterseparation inflating them individually with pressurised gas so as toconform them to the mould cavity and so form the shaped articles. Such aprocess in its basic form, usually referred to as "blowmoulding", isused, inter alia, for the manufacture of bottles for household andindustrial use, in applications where the internal pressure is to belittle or no greater than atmospheric pressure or, in other words, thereis little or no over-pressure. Bottles for carbonated beverages,however, may be required to withstand over-pressures of severalatmospheres, and for such bottles a modification of the basicblowmoulding process, usually referred to as "stretch-blowmoulding", isused. In this proces the individual lengths of extruded tube arestretched mechanically in their longitudinal direction prior to, or atthe same time as, they are inflated; in a variation, injection-mouldedpreforms are used instead of the lengths of extruded tube. Thelongitudinal stretching together with the circumferential stretchingwhich occurs during inflation molecularly orientate the bottle materialboth longitudinally and circumferentially of the bottles; this biaxialorientation gives the bottles the strength necessary for them towithstand the high over-pressures which may be generated by carbonatedbeverage products.

Another kind of container which may be subject to substantialover-pressures is the conventional three-piece food can, which is liableto over-pressure during processing by the food packer and/or duringreheating by the consumer. Such cans are typically made of tinplate.This material is becoming expensive.

SUMMARY OF THE INVENTION

It is the Applicants' belief that by making the tubular can wall ofbiaxially oriented plastics material instead of metal the cost of thearticles as a whole can be reduced without any substantial impairment ofthe ability of the can to withstand the overpressures to which it may besubjected. In addition to the cost advantages of the material itself,the use of thermoplastics material for the can wall may provideadditional advantage in the ease of handling and storing the bulkmaterial, the speed and relative quietness of the manufacturing process,and the consumer appeal of the finished can.

In accordance, therefore, with one aspect of the invention there isprovided a container having a tubular wall of biaxially orientedthermoplastics material, and end closures closing the ends of the wall.The end closures may be of a metal such as tinplate or aluminium,although this is not essential. They may be attached releasably orotherwise.

Although such a container is of particular application to the packagingof processed foods, (in which case the thermoplastics material should bedimensionally stable at the processing temperatures which are to beused), this is not its only application. It might for example, be used,for carbonated beverages which may require no processing; furthermore,although the biaxial orientation of its wall makes it particularlysuited to applications in which high overpressures are encountered, theenhanced physical characteristics provided by the biaxial orientationmay be of value for containers which are required to withstand neitherthermal treatment nor substantial overpressure.

Advantageously, one of the end closures of the container is of theeasy-opening variety, having a removable portion which may be torn awayby the user. Usually the easy-opening end closure will be of metal andof the restricted opening type for carbonated beverages, of the "fullaperture" type for other products such as processed foods.

The tubular wall for the container may be manufactured by conventionallyforming a shaped tubular article by stretch-blowmoulding, and cuttingthe article to provide one or more parts each suitable as the tubularwall of a container. However, such a method of manufacture is inherentlyslow and energy expensive in that a substantial part of the tubulararticle is not of the required shape or thickness. Applicants havedevised a process by which to produce a tubular article of biaxiallyoriented thermoplastics material, of which an incresed proportion issuitable for forming tubular walls for containers. Accordingly, from asecond aspect, the invention provides a process for forming at leastpartly biaxially oriented tubular articles from an elongate tube ofthermoplastics material, which comprises repeatedly performing a cycleof operations each including the following steps:

engaging the tube by a first clamping means over a first region at aleading end of the tube and by a second clamping means over a secondregion at a spacing from the first region, so as to define between theclamping regions a portion of the tube to be longitudinally stretchedand radially expanded;

moving the clamping means apart to stretch the tube portionlongitudinally and admitting pressure fluid to the tube portion toexpand it radially, such stretching and expansion forming a bubble ofbiaxially oriented thermoplastics material adjacent the leading end ofthe tube; and

severing at least a substantial part of the bubble from the tube to formthe tube with a new, radially outwardly flared, end as the said leadingend of the tube for the succeeding cycle of operations.

The word "bubble" here and henceforth in the specification and claims isnot to be considered as necessarily denoting a substantially closedbody. As manifest from the embodiment particularly described, it may beopen at its end remote from the end at which it is, or was, connected tothe tube.

In addition to a process as defined in the above paragraph, theinvention also provides, from a third aspect, apparatus for forming atleast partly biaxially oriented tubular articles from an elongate tubeof thermoplastics material by a repeated cycle of operations, theapparatus comprising

a first clamping means arranged for engaging a leading end of the tubeover a first clamping region,

a second clamping means arranged for engaging the tube over a secondclamping region at a spacing from the first, the first and secondclamping means being relatively reciprocable longitudinally of the tube,

stretch means to move the clamping means apart with the tube engagedthereby so as longitudinally to stretch the portion of the tube lyingbetween the clamping regions,

fluid pressure means operable to supply pressure fluid to the interiorof the tube portion so as to expand it radially, such stretching andradial expansion forming a bubble of biaxially oriented thermoplasticsmaterial adjacent the leading end of the tube, and

severance means operable to sever at least a substantial part of thebubble from the tube to form the tube with a new, radially outwardlyflared, end as the said leading end of the tube for the succeeding cycleof operations.

Although they have particular value in the manufacture of tubular, inparticular right-cylindrical walls for containers, the above-definedprocess and apparatus are not to be considered as limited to such anapplication, but may be applied to the manufacture of other tubulararticles from thermoplastics material which is at least partly biaxiallyoriented.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and features of the invention will becomeapparent from the following description, given by way of example andwith reference to the accompanying drawings in which:

FIGS. 1 to 5 diagrammatically show individual stages in the operatingcycle of an apparatus in accordance with the invention to produce atubular bubble of biaxially oriented thermoplastics material;

FIG. 6 shows a container having its cylindrical wall cut from thetubular bubble; and

FIGS. 7 to 11 variously show the arrangement of a particular apparatusarranged to operate by the operating cycle of FIGS. 1 to 5; accordingly,the same reference numerals as FIGS. 1 to 5 are used to denote analogousparts. Of FIGS. 7 to 11 individually:

FIG. 7 shows the apparatus in side elevation;

FIG. 8 shows the apparatus in plan view;

FIG. 9 shows the apparatus in end elevation taken in section on the lineIX--IX in FIG. 7;

FIG. 10 is an enlarged view of the apparatus taken in centrallongitudinal section at the end of a bubble-forming operation, showingthe upstream end of the mould and the associated clamping arrangementfor the tube material; and

FIG. 11 similarly shows the downstream end of the mould and theassociated arrangements for clamping the free end of the tube at thebeginning of an operating run and thereafter.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIGS. 1 to 5, an apparatus for forming tubular articlesis arranged to perform repeated cycles of operation upon the right-handend of a length of extruded tube 10 of PET (polyethylene terephthalate)material which is in a heat-softened amorphous condition.

FIG. 1 shows the apparatus at the beginning of an operating cycle. Theleading end of the tube is flared from the previous cycle, and theflared portion 10' is clamped around its periphery by co-operation of adisc-like clamping member 11 on its inside and, on its outside, theleading or downstream ends of two mould halves 12 which are verticallyseparable as will later become apparent. The clamping member 11 andmould halves 12 thus form a clamping arrangement for the tube.

In addition to their vertical separation, the mould halves 12 aretogether reciprocable longitudinally in relation to the tube through adistance substantially equal to their length. At the moment of timedepicted in FIG. 1 they are at the left hand (i.e. upstream) extremityof their longitudinal movement; also, they are closed to theircavity-forming condition.

In addition to the clamping member 11 and the mould halves 12, theapparatus further comprises a second clamping arrangement for the tube.This second clamping arrangement has an elongate mandrel 13 whichextends horizontally from an actuator (not shown) on the right of theapparatus, through the centre of the clamping member 11, and terminatesat a rounded free end 20 which at the condition of the apparatus shownin FIG. 1 is engaged in the mouth of the tube 10 proper at the base ofthe flared portion 10'. The mandrel is longitudinally reciprocable bymeans of its associated actuator (not shown), the position shown in FIG.1 being its fully extended position. In general, it is freely slidablethrough the clamping member 11.

For co-operation with the mandrel to clamp the tube material theapparatus has an annular split collar 14 which in FIG. 1 is disposedwith the mould cavity defined by the mould halves 12. For the purposesof the following description of collar should be considered as fixed inlongitudinal position. The collar may be contracted by means not shownto clamp the tube material against the leading end of the mandrel, butit is to be understood that in the FIG. 1 condition of the apparatus thecollar is open and the tube is free to move through it.

Following the clamping of the periphery of the flared portion 10'between the clamping member 11 and the mould halves 12, the mould halves12 are moved horizontally to the right through a predetermined distance,carrying with them the clamping member 11 and the tube 10. Apredetermined length of the tube is therefore drawn through the collar14 without stretching.

When the condition depicted in FIG. 2 has been reached the collar 14 isclosed onto the tube 10 to clamp it against the mandrel 13. The portionof the tube then present within the mould is thereby clamped at its lefthand end in addition to being clamped at its right hand end. Furtherrightward movement of the mould halves 12 and the clamping member 11 asbefore then causes this tube portion to be stretched longitudinally. Atthe same time as this longitudinal stretching is taking place, air athigh pressure (e.g. 250 to 300 psi) is admitted to the interior of thetube portion so as to expand the tube portion radially into conformitywith the mould cavity as a bubble at the leading end of the tube 10immediately behind the flared portion 10'. Typically the stretch ratiosachieved, that is to say, the ratios of the dimension when stretched tothe original unstretched dimenisons, are 2:1 in the axial direction and4:1 in the radial direction. In the drawing the tube bubble is denotedby the reference number 100.

In known manner the combination of axial and radial stretching causesmolecular orientation of the tube material in those directions, thusgiving enhanced physical characteristics to the tubular article orarticles which are to be formed from the bubble as is later to bedescribed.

FIG. 3 shows the end of the stretch-blow operation, which occurs whenthe mould halves reach their righthand limiting position. The tubewithin the mould is then fully stretched and in conformity with themould cavity.

The FIG. 3 condition of the apparatus may be held for a period to allowthe expanded tube material to harden, after which the tube bubble isvented to reduce its internal pressure to approximately atmosphericpressure, and the mould halves 12 are vertically separated to thepositions 12' indicated by dashed lines in FIG. 3, so as to release thetube bubble for severance and ejection.

Severance of the bubble from its parent tube and subsequent ejection ofthe bubble are effected as shown in FIGS. 4 and 5. After the mouldhalves 12 have been separated they are moved to their upstream positions(FIG. 4), and a pair of opposed, contoured gripper members, one of whichis shown in FIG. 4 and denoted by the reference numeral 21, are movedhorizontally towards one another to positions in which they support thetube bubble gently but firmly between them. A knife is then operatedtransversely of the apparatus so as to sever the tube bubble from theparent tube 10, leaving the latter with a new flared leading end 10' forthe subsequent operating cycle of the apparatus. For clarity, the knifeis not shown in the drawings, but its position is indicated by the lineof severance 22 separating the tube bubble from the parent tube. Inorder to facilitate cutting, the knife may be heated an/or a smallpositive pressure may be provided within the tube bubble to resist anytendency for the bubble to be collapsed inwardly by the knife. It willbe understood from the drawings and the preceding description that afterseverance the "bubble" is substantially right-cylindrical.

After the bubble 100 has been severed, and while it is still held by thegripper members 21, the disc 11 and the mandrel 13 are withdrawn toretracted positions (FIG. 5) in which they are clear of the bubble,following which the gripper members are moved apart to allow the bubbleto fall onto a suitable take-away device (not shown) such as ahorizontal conveyor. The apparatus is then prepared for its next cycleof operations by advancing the clamping member 11 and mandrel 13 intoengagement with the tube 10 at, respectively, the periphery and root ofthe flared end 10', and subsequently closing the mould halves 12 toclamp the flared end against the clamping member. The collar 14, whichhad been closed onto the tube for the stretch-blow operation to form thebubble 100 as described above, is opened for the new operating cycle ata convenient time; desirably it is held closed for the severanceoperation, so as to assist the gripper members 21 and the clampingmember 11 to hold the tube and its bubble firmly in position while theknife is operating.

The bubble 100, after ejection from the apparatus, has its ends croppedto remove any flawed material and may then be subdivided into two ormore lengths if desired. The one or more lengths of biaxially orientedtube so produced ar substantially right-cylindrical and transparent, andmay be used as the bodies of food containers. Typically for such anapplication, and as shown in FIG. 6, they are closed at each end bymetal end closures 30, 31 which are glued, heat-bonded, and/or crimpedinto position; in FIG. 6 the closure 31 is shown to be of thefull-aperture easy-open variety. If the containers are intended to beprocessable, that is, they are intended to be sterilised or pasteurisedtogether with their contents, the length or lengths of biaxiallyoriented tube are held for a time at a temperature at least equal to,and preferably somewhat greater than, the sterilisation orpasteurisation temperature which is to be used whilst restrained fromshrinking beyond their desired circumferential and longitudinaldimensions. In known manner this thermal treatment heat-sets the lengthor lengths of tube so that they are dimensionally stable during thesterilisation or pasteurisation process. The thermal treatment can becarried out before or after the lengths of tube have been cut from thebubble 100, and it is envisaged that the restraint required for the tubematerial during the treatment can be effected by pressurising thebubble.

A stretch-blow apparatus as shown in the drawings and described abovemany be linked directly with an extruder by which the tube 10 iscontinuously produced. In order for the cyclic operation of theapparatus to be correlated with the substantially constant speed of thetube in relation to the extruder, the extruder and/or the apparatus maybe arranged to reciprocate in synchronism with the operating cycle ofthe apparatus; alternatively a take-up mechanism may be interposedbetween the extruder and the apparatus to convert the tube movement fromthe constant speed output of the extruder to the intermittent inputmovement required by the apparatus. In this way the apparatus may bearranged to automatically and repetitively produce bubbles 100 from atube 10 continuously produced by the extruder.

In order to condition the tube for the stretch-blow operation, the tubeemerging from the extruder is rapidly cooled (for example by a waterbath) to approximately room temperature, the rate of cooling being suchthat the tube material maintains its amorphous condition. After coolingthe tube is reheated by gas burners (for example) to the temperaturesrequired for the stretch-blow operation. Typically the tube emerges fromthe extruder at 572° F., and after cooling is reheated to a temperaturewithin the range 190° F.-250° F. for the stretch-blow operation. Ifdesired, the apparatus may have provision for heating and/or cooling thetube to achieve temperture control.

Although the apparatus of FIGS. 1 to 5 is shown and described inrelation to a tube 10 which is caused to move along a horizontal path,it may with advantage be arranged to operate upon a tube 10 whichdescends on a vertical path; FIGS. 1 to 5 should then be considered asbeing individually turned through 90° in a clockwise sense. With such anarrangement the tube extruder, if linked directly with the apparatus,may be mounted vertically above the latter, thereby facilitating thecontrol of the tube in its movement between the extruder and theapparatus.

Reference is now made to FIGS. 7 to 11, which show a specificarrangement of the apparatus diagrammatically featured in FIGS. 1 to 5.

The apparatus has two horizontally spaced frame members 30, 31 supportedby vertical legs 60 with feet 61, and between which extend a pair ofhorizontal and parallel guide rods 32.

A carriage 33 has guide blocks 42 by means of which it is guided forreciprocating horizontal movement along the guide rods 32 in response toa pneumatic actuator 34 having its cylinder 63 mounted outside the framemember 31. The piston 35 of this actuator extends horizontally throughthe frame member 31 to connection with the carriage 33 at a coupling 36arranged to allow free vertical tilting movement between the piston andthe carriage.

The carriage 33 carries the two halves 12 of the mould for the tube 10,the latter being visible in FIGS. 7, 8 as it enters the apparatus fromthe left. The mould halves, which are shown in their closed position,are vertically separable by means of a further pneumatic actuator 37having its cylinder 38 pivotally mounted on the carriage at a mountingbracket 39. The piston 40 of the actuator 37 is arranged to operate onthe two mould halves simultaneously, to lower the lower mould half andraise the upper mould half. For that purpose a head 41 mounted on theend of the piston 40 is pivotally connected by a horizontal spindle 43to yokes at the top ends of two bifurcated link members 44 disposed oneto each side of the head. The arms of the link members are cranked, eachhaving a top end portion which is inclined in the direction away fromthe actuator 37, and a bottom end portion which extends vertically tothe free end of the arm at the bottom of the link member.

Midway along the bottom end portions of their arms, the link members 44are pivoted on respective spindles 45 journalled in mounting blocks 46for movement about a common horizontal axis which is fixed in relationto the carriage 33. Pivotal movement of the link members as the actuator37 is operated is transmitted to the mould halves 12 by means of a pairof short connecting plates 47 for the upper mould half and a pair oflonger connecting plates 48 for the lower mould half. Each link member44 is associated with one plate 47, 48 from each pair for a respectiveside of the mould.

The plates 47 are rectangular and vertically disposed; they are boltedto the upper mould half 12 at their bottom ends and at their top endsare pivotally attached to the link members 44 by spindles 50 locatedbelow the spindles 45. The plates 48 are C-shaped and disposed so as toembrace, with clearance, the associated plates 47; they are bolted tothe lower mould half at their bottom ends and at their top ends arepivotally attached to the link members 44 by spindles 50 located abovethe spindles 45. At each side of the mould the spacings of the spindles50, 52 from the associated spindle 45 are equal, so that operation ofthe actuator 37 causes equal and opposite movements of the mould halvestowards or away from one another. Extension of the actuator causesseparation of the mould halves, the available movement being sufficientto free the mould halves individually from a tube bubble 100 previouslyformed within the mould and to allow the mould halves to be subsequentlymoved to an upstream retracted position. A positive limit to theseparating movement is provided by washers 53 on sleeved studs 54.

The mould is shown in the drawings in the downstream, closed conditionwhich it has at the end of a moulding operation. It then encloses theright hand extremity of a horizontally disposed, circular tube 65 whichis cantilevered at its left hand end from the frame member 30. The mouldin its upstream, retracted position is in telescoped relation to thistube.

A circular sleeve member 66 slidable along and within the tube 65projects beyond the frame member 30 where it is linked by diametricallyopposed trunnion pins 67 to a horizontal operating arm 68. Thisoperating arm is pivoted to the machine frame at 69 and its oppositefree end is attached to the piston 70 of a pneumatic actuator 71 havingits cylinder mounted on the frame member 30. It will be understood thatoperation of this actuator will cause the sleeve 66 to slide along andwithin the tube 65; the purpose of such movement will now becomeapparent from the following description which is given with particularreference to FIG. 10.

FIG. 10 is an enlarged view of the end of the tube 65 remote from theframe member 30. The end of the tube is provided by a circular endpiece73 which is attached to the end of the tube proper and has a centralaperture 74 dimensioned for the thermoplastics tube 10 to pass throughit. Around the aperture the endpiece presents a plane wall 75 to thetube interior; in the downstream direction of the apparatus it presentsa frustoconical face 76 which diverges from the orifice 74 to theendpiece periphery.

The plane wall 75 of the endpiece provides the reaction face for anannular split collar 14 formed of three identical collar elements 80each occupying somewhat less than 120° of the collar circumference andof which two are visible in FIGS. 7 and 10. The collar elements areshaped to provide for the collar a frustoconical external surface 81which faces outwardly and along the tube 65, and a central aperture 82which is aligned with the aperture 74 of the endpiece 73.

Compression springs 83 (FIG. 7 only) between adjacent ones of the collarelements 80 bias the collar elements apart so that the segmentedfrustoconical surface 81 of the collar is held in camming engagementwith a complementary frustoconical surface 84 formed on the end of thesleeve 66. When the actuator 71 is retracted, that is, when the sleeve66 is at the leftmost end of its travel (as seen in FIGS. 7 and 8), thecentral aperture 82 of the collar is of the same diameter as the centralaperture 74 of the endpiece, and the tube 10 can move freely throughboth apertures. However, by extending the actuator 71 to move the sleeve66 to the right, the collar 14 is contracted and the aperture 82 isclosed down to a diameter which is somewhat smaller than the externaldiameter of the tube 10. The collar therefore engages the tube peripheryas desicrbed in relation to FIGS. 1 to 5.

In addition to the tube 65, the sleeve 66, and the mould formed of themould halves 12, FIG. 10 shows the mandrel 13 in the extended positionin which it engages the interior of the thermoplastics tube 10 withinthe collar 14 so as with the collar to form a clamping arrangementenabling the portion of the tube 10 lying within the mould halves 12 tobe stretched and simultaneously blown to form the tube bubble 100.

The mandrel 13 is the piston, of a pneumatic actuator 90 having itscylinder 91 mounted on the frame member 31 beneath the cylinder 63 ofactuator 64. For engaging within the tube 10 it has a nose 92 of theappropriate diameter screwed onto its free end. A flexible annularsealing washer 93 is located in a peripheral groove 94 formed around themandrel immediately behind the nose so as to form a seal with theinterior of the tube 10 and thereby prevent the escape of pressurisedfluid along the interface between the nose 92 and the tube when thebubble 100 is being formed.

FIG. 11 shows the clamping member 11 in its engagement with the mouldhalves 12 to clamp the periphery of the previously flared end 10' of thetube 10 for the formation of the bubble 100. The clamping member has acircular body 101 formed with a central aperture 102 through which themandrel 13 passes with a small clearance 124. Interconnected ports 103,104 provide a passage through which the pressurised air required forblowing the bubble may be fed to the interior of the tube 10 via thisclearance from a suitable supply (not shown). A sealing ring 105 engagesthe mandrel 13 to prevent escape of the pressurised gas along theclearance in the opposite direction.

To assist the clamping member 11 initially to enter the flared end ofthe tube 10, the clamping face 106 on the body 101 of the clampingmember is frustoconical, and the flared end itself has an enlargeddiameter by virtue of a groove 150 which extends around the mould cavitywhere the flared end is formed. The clamping face provided on the mouldhalves 12 for co-operation with the clamping face 106 is denoted 107.

Features of the apparatus other than those described above will becomeapparent from the following description of the apparatus in operation.Initially it will be assumed that with the mould open and at the lefthand end of its travel as seen in FIGS. 7 and 8, the last tube bubble100 to be formed has just been severed from the tube 10 and ejected fromthe apparatus. At this time the end of the tube 10 left remaining isflared, its free edge being located at the position indicated by thedashed line 110 in FIG. 10 within the groove 150; moreover, the mandrel13 is in a retracted position with the clamping member locatedlongitudinally on it by a spring-loaded ball 111 (FIG. 11) engaged in adetent 112 (FIG. 10) on the mandrel.

The actuator 90 is extended to engage the clamping member 11 within theperiphery of the flared end of the tube 10, and to engage the nose 92within the tube at the base of the flared end. The clamping memberengages the tube before the nose so that during the latter part of themandrel movement the ball 11 is forced out of the detent 112 andthereafter the mandrel slides freely through the clamping member.

After the actuator 90 has been extended the mould halves are closed byextension of the actuator 37 to clamp the flared end of the tube againstthe clamping member 11, whereupon the actuator 34 is retracted to movethe mould progressively to the right as seen in (FIGS. 7 and 8),carrying the clamping member 11 with them. During an initial part ofthis movement the collar 14 is open so that the tube 10 is drawn freelythrough it and over the mandrel 13. However, at a predetermined positionof the mould halves in their rightward movement, the actuator 71 isextended to close the collar 14 onto the tube 10 after which continuedmovement of the mould halves stretches the portion of the tube lyingwithin the mould while pressurised air is simultaneously admitted to theinterior of the tube via the ports 103, 104. In this way a bubble 100conforming to the interior of the mould is formed on the tube, asdepicted in FIGS. 10 and 11 which respectively show the left and righthand ends of the mould at the end of the bubble formation.

After the thermoplastics material of the bubble has solidified the mouldhalves 12 are seperated by the actuator 37 and returned to theirupstream, retracted positions by the actuator 34, leaving the bubble 10supported at its left hand end by the endpiece 73 and at its right handend by the clamping member 11. A pair of opposed gripper members 21 arethen simultaneously operated by pneumatic actuators 120 to grip thebubble firmly but gently while a knife 121 (FIG. 9) operated by afurther actuator (not shown) severs the bubble along the line 110 (FIG.10) to free the bubble from the tube 10 leaving the latter with a flaredend for the succeeding cycle of operations.

The mandrel 13 is then retracted by the actuator 90 to withdraw it fromthe severed bubble 100. As the mandrel approaches the end of itsmovement the ball 111 re-engages in the detent 112 so that the clampingmember 11 moves with the mandrel out of engagement with the bubble,leaving the bubble free to fall away for cropping and subdivision asdesired when, later, the gripper members 21 are retracted by respectiveactuators 120.

Following ejection of the bubble 100, the mandrel 13 is advanced toengage the tube 10 with its nose 92 and with the clamping member 11 aspreviously described. The cycle of operations described above isrepeated to form the next bubble 100. In passing it will be noted thateach bubble as severed from the parent tube 10 incorporates, in usableform, a large proportion of the flared end 10' left on the tube when thepreceding bubble is severed. It is hoped that the percentage of the tube10 material which is unusable in the severed bubbles can be reduced to2% or below.

For the first cycle of an operating run, the apparatus may be requiredto operate upon a tube 10 which initially is not flared at its leadingend. The clamping member 11 and mould halves 12 are then incapable ofachieving the required clamping engagement at their clamping faces 106,107, but instead the clamping member 11 is itself arranged to clamp theleading end of the tube to enable the first bubble 100 to be formed.

From FIG. 11 it will be seen that the clamping member 11 has a blindannular opening 122 facing in the upstream direction of the tube 10 inconcentric relation with the aperture 102 for the mandrel 13. Radiallyon its inside the opening is defined by a clamp sleeve 123 which is fastwith the body 101 of the clamping member and forms part of the clearance124 with the mandrel 13. Radially on its outside the opening 122 isdefined by three identical clamping elements which are held captive by aface plate 140 on the body 101, and each of which occupies somewhat lessthan 120° of angle. The clamping elements, of which two are visible andindicated by the reference numeral 125, have clamping projections 140and are biassed outwardly away from one another by compression springs(not shown) between adjacent elements; they are guided individually forradially inwardly movement in relation to the opening 122 by lands 126which are engaged in radially directed grooves formed in the body 101.One of the side faces of one such groove is shown in FIG. 11 in relationto the associated land 126, and indicated by the reference numeral 127.Each clamping element has an associated rotatable shaft 128 which isjournalled in the body 101 and which mounts a pulley 129. The pulleys ofthe three elements are linked by a non-slip belt 130 (FIG. 7). Theuppermost one of the shafts 128 is extended beyond the pulley 129 andcarries an actuating lever 130 arranged for engagement, when the mouldhalves are brought together, by a resiliently-mounted plate (not shown)mounted on the upper mould half.

Each shaft 128 is machined with a flat 131. The clamping elements 125make camming engagement with their associated flats, so as to bedepressed radially inwards against the action of the springs when theshafts 128 are turned.

In the radially depressed position of the clamping elements the clampingprojections 140 are capable of clamping the unflared end of a tube 10received within the opening 122 against the clamp sleeve 123.

It will thus be understood that when, as previously described, the mouldhalves are in their upstream, retracted positions and the actuator 90 isextended to insert the mandrel nose 92 within the tube 10, the unflaredend of the tube enters the opening 122 so as to be held securely therewhen the mould is closed by engagement by the projections 140.Subsequently, the mould is moved in the downstream direction and abubble 100 is formed from the tube 10 in the manner described above,with the difference that the free end of the tube is gripped within theopening 122 instead of between the clamping faces 106, 107. After thefirst bubble 100 of the operating run has been formed and ejected, thetube 10 is flared for each of the subsequent bubbles.

Although in the apparatus described with reference to FIGS. 7 to 11 eachbubble 10 is severed from the parent tube 10 at a position such thatpart of the bubble is left as the flared end of the tube for thesucceeding cycle of operations, this is not essential to the invention;it is possible for the tube end to be unflared for each cycle ofoperations, and for each bubble to be severed from the tube completely.The apparatus shown in FIGS. 7 to 11 could, for example, be modified tooperate in this way by arranging the knife 121 to operate on the tubebetween the collar 14 and the endpiece 73 to sever the bubbles 100individually from the tube, and by advancing the tube 10 to feed itsfree end into the opening 122 for each bubble-forming operation.

Furthermore, although the bubbles 100 produced by the describedapparatus are cropped and then used (with subdivision or otherwise) toform one or more tubular bodies for containers, a tubular articleproduced by a method or apparatus in accordance with the invention mayhave utility in its own right, (i.e. without cropping or subdivision).The bubble may be cut from the parent tube so as to have a portion ofthe tube at each end; one or both of the portions of tube maysubsequently be formed, for example, with screw threads for receiving ascrew closure. In one possible application the bubble is provided withportions of the unexpanded tube at each end and is cut in half to formtwo bottle-like articles each having a reduced-diameter neck and an openend, the articles are individually provided with end closures of metal,paper and or plastics to close the open ends, and screw-threads to takescrew closures are formed on the necks either before or after the bubbleis subdivided.

What is claimed is:
 1. A process for forming at least partly biaxiallyoriented tubular articles from an elongate tube (10) of thermoplasticsmaterial having a first predetermined cross-sectional dimension, theprocess comprising repeatedly performing a cycle of operations eachincluding the following steps:engaging the tube by a first clampingmeans (11, 12) over a first region at a leading end (10') of the tubeand engaging the tube by a second clamping means (13, 14) over a secondregion at a spacing from the first region so as to define between theclamping regions a portion of the tube to be longitudinally stretchedand radially expanded; and moving the clamping means apart to stretchthe tube portion longitudinally and admitting pressure fluid to the tubeportion to expand it radially to a second predetermined cross-sectionaldimension greater than the first predetermined cross-sectionaldimension, such stretching and expansion forming a bubble (100) ofbiaxially oriented thermoplastics material adjacent the leading end ofthe tube; characterized by severing a substantial part, but not all, ofthe bubble from the tube to leave the tube with a radially outwardlyflared end, having the second predetermined cross-sectional dimension,at the leading end of the tube, and engaging the flared end, having thesecond predetermined cross-sectional dimension, of the tube by the firstclamping means during the succeeding cycle of operations.
 2. A processaccording to claim 1, characterized in that for each cycle of operationit includes the further step of confining the tube portion within amould cavity (12) during its stretching and expansion to form thebubble, the bubble thereby being conformed to the mould cavity by thepressure fluid.
 3. A process according to claim 1, characterized in thatthe second clamping means (13, 14) engages the tube on the tube outsideand sealingly on the tube inside while maintaining the tube in an opencondition at the second region.
 4. A process according to claim 1, whichis further characterized by subdividing each severed bubble to formthereform one or more parts as the tubular articles.
 5. A processaccording to claim 4, characterized in that the or each part of eachsevered bubble is or right-cylindrical form.
 6. A process according toclaim 4, which is characterized by the further step of forming the oreach part of each severed bubble as a container by attaching a closuremember (30, 31) to each end thereof.
 7. A process according to claim 6,characterized in that the or each container is heat-processable togetherwith its contents, wherein the process further comprises subjecting thethermoplastics material of the respective severed bubble part to a heattreatment whilst it is restrained against excessive dimensional change,the heat treatment being such as to give the thermoplastics materialdimensional stability at the processing temperature to be employed.
 8. Aprocess according to claim 1, characterized in that the thermoplasticsmaterial is polyethylene terephthalate.
 9. A process according to claim2 characterized in that the second clamping means (13, 14) engages thetube on the tube outside and sealingly on the tube inside whilemaintaining the tube in an open condition at the second region.
 10. Aprocess according to claim 2, which is further characterized bysubdividing each severed bubble to form therefrom one or more parts asthe tubular articles.
 11. A process according to claim 3, which isfurther characterized by subdividing each severed bubble to formtherefrom one or more parts as the tubular articles.
 12. A processaccording to claim 5 which is characterized by the further step offorming the part of each severed bubble as a container by attaching aclosure member (30, 31) to each end thereof.
 13. A process according toclaim 2, characterized in that the thermoplastics material ispolyethylene terephthalate.
 14. A process according to claim 3,characterized in that the thermoplastics material is polyethyleneterephthalate.
 15. A process according to claim 4, characterized in thatthe thermoplastics material is polyethylene terephthalate.
 16. A processaccording to claim 5, characterized in that the thermoplastics materialis polyethylene terephthalate.
 17. A process according to claim 6,characterized in that the thermoplastics material is polyethyleneterephthalate.
 18. A process according to claim 7, characterized in thatthe thermoplastics material is polyethylene terephthalate.